Static hydraulic continuously variable transmissions have been used in various applications. As an example, a static hydraulic continuous variable transmission is disclosed in Japanese Patent Publication No. 93661/1989. The continuously variable transmission disclosed therein uses a fixed swash plate type hydraulic pump and a variable swash plate type hydraulic motor to perform continuously variable transmission control by variably controlling a swash plate angle of the motor. A motorcycle including the static hydraulic continuously variable transmission is also disclosed. A shift control apparatus to perform the swash plate angle control of a motor is formed of a motor (swash plate actuator), a reduction gear apparatus, and a ball-nut mechanism (rotation-linear movement converting mechanism), and is positioned to extend to the external side of the rear part of the continuously variable transmission housing.
However, the shift control apparatus described above is provided with the swash plate actuator formed of a motor or the like in the manner being extended to the external side from the rear part of the continuously variable transmission. The swash plate actuator provides a protection cover which covers the swash plate actuator in order to eliminate exposure to splash water from the lower side of the body, rain water, and dust or the like from the front side. However, this shift control apparatus also requires that the size of the extension to the external side to be increased due to the protection cover and, therefore, the cooling property (air-cooling characteristic) of the swash plate actuator is deteriorated.
Particularly, as is disclosed in Japanese Patent Publication No. 93661/1989, in structures where the swash plate actuator is extended toward the rear side and adjacent to a drive chain for transmitting the driving force to the rear wheel while it is mounted to the motorcycle, the actuator is likely to receive the splash water from the lower side of the body when it is running or to allow adhesion of oil splashed from the drive chain. Moreover, a swing arm is also provided for the motorcycle in order to support the rear wheel, but here rises a problem that the shape of swing arm is restricted in order to eliminate interference between the swing arm and the swash plate actuator. It is also thought to provide the swing arm to the rear side of the body in view of avoiding such interference, but in this case, a new problem is created in that the total length of the body becomes longer.